The prior art includes a variety of techniques and interconnect structures for connecting semiconductor chips to circuit boards, other devices, substrates, etc. For example, solder beads are often used to connect flip chips to external circuitry. Such solder beads are typically disposed in a conductive recess or terminal of the flip chip and reflowed to form a bead for connecting to external devices, such as a circuit board. Such solder beads are typically formed from lead or lead alloy. Recently, silver has been used to replace lead to lessen any impact of discarded chips on the environment.
Another process for forming solder connections is the creation of a pillar interconnect with a solder bead formed atop the pillar interconnect. The pillar interconnect is typically disposed over a contact pad of the semiconductor device and extends upward. An array of such pillar interconnects can be fabricated with a very small pitch to accommodate high density applications. The solder beads of the array can then be coupled to the external circuitry using reflow techniques.
When using pillar interconnects, any force imparted by the external circuitry is transmitted to the pillar interconnects. In turn, the pillar interconnects transmit the force to the semiconductor device at the coupling site between the pillar interconnect and the device. As compared to solder beads disposed directly in the chip (using conventional techniques), the pillar interconnects have a narrower base, resulting in a greater stress being imparted on the semiconductor device. The resulting strain can manifest itself in myriad undesirable ways, such as cracking or delamination of certain materials.